Pulse discriminating circuit



Jan. 20, 1953 L. W. ALVAREZ PULSE DISCRIMINATING CIRCUIT Original Filed March 18, 1943 RECEIVER TIMING GENERATOR R E T n M s N A R T INVENTOR LUIS W. ALVAREZ RADIO ECHO DETECTION SYSTEM ATTORNEY Patented Jan. 20, 1953 UN-I TED ES v 1 2,626,352

PtiLs'E' iiiscRimNATI'NG cream fAlv'arez, Berkeley, Calili, assiniir; by

nde'siiefas'si'giiments, to the Uaitea'ststesw America re resented by thesecrtai'y of the Navy e-rear:agrarian-' March-18,1943;

7g.s25',,nowratem No.2,568,265,"'da ember 18, 19 51. Divided and this application August 15, j1"949, 'seriar-No.-'-110;295

'2" Claims. (01; 250 -27) This invention? relates to i 'adiofbeacon' systems I which'are 'ncrmany inoperative but" Whibh'maybe fired from a remote "point" by" radio i Signals, and

"more particularly to a pul s'e discriminating circuit for use in the'receiv'erof' a beacon system wherebythe beacon willfbe' fired only whe'n'it receives'a signal of a predetermined character.

This appne tien is "a division of my eo-pending application Serial No.' 179,'625, filed March 18,

1943, e1ititled fRadid'Beacgn and System Utilizing It, now Patent No'.2,568,2'65, issued'Sepscription when consideredwith the accompanying drawings in which: i Fig. lis a blockdiagram' of abeacon'system inwhich the'circuit of the invention finds'particularapplication; and

Fig. 2 is a circuit diagram of the discriminating circuit of the present invention.

Referring now to Fig. 1, a beacon system in which the circuit of the present invention may be utilized is shown as comprising a transmitter In which is provided with a suitable antenna II for radiating electromagnetic oscillations, which are preferably in the microwave region. A timing generator i2 is connected to the transmitter and is arranged to modulate the oscillations produced thereby in a predetermined manner so that a coded signal may be radiated from the antenna. For purposes of illustration, the signal modulated upon the carrier waves has been indicated at 13 as two long pulses with a short pulse in between them, represented by the letter K in the International Morse Code, and these pulses are fast enough so that the total time of the coded signal will be in the order of 100 microseconds. However, since this signal and the means for generating it do not form a part of the present invention, they will not further be described here- 1n.

A receiver 14 which is connected to the timing generator I2 is also suppliedwith an antenna l whereby it may pick up signals broadcast from some remote point as, for example, from the transmitter of a radio echo detection system 30 which may be located on a moving craft at some remote point. This remote system is preferably provided witha directionalantenna 21;mounted for rotation "on the rotating structure "'38. "The receiver [4' is arrangedto"respond onlyto'isignals of a predetermined :chaiaterflas for instance, double pulse modulation," as indicated at 'I 6,the carrier freit ue'ncy''being the' frequency to which the receiver Mistuned. "The response of "the receiver is used "to 'controlthetransmitter 10 whereby the latter is only operating immediately after the reception by' ther'eceiver of oneof the double pulses 'I 6 and then in'a manner" and for a period of timesuifieientonly to radiatethe coded signal 'ISaft'er'Which'the transmitter is shut ofi'. Therefore,- whena doublepulseatthe proper'carrier wave frequency is picked up by the receiver I4, it fi'r es'the transmitter 10, radiating a single codedsignal, as determined by the timing generator l2. e

Referring now to Fig, 2," a 'disc'riniinatingbir- 'cuit for causing the receiver [4 t respond only to 'the double pulse 'I6"'isfilliistrated. *This' circuit comprises two tubes 1 1 'andl 8 upon the grid'ci'rcuits of which'thedouble pulse HiiS applied, preferably in an inverted form' as 'indi'catedfso that the signal received e the grids is negative.

' This'negative doublepulseis' applied directly to the grid of the tube ll, but the grid of the tube is is provided with a delay circuit which includes inductances I9 and condensers 20. The values of inductances l9 and condensers 20 are so chosen that the signal reaching the grid of the tube [8 will be delayed a time interval equal to the time between individual pulses of the double pulse signal. When the values of these components are properly chosen, the first portion a of the double pulse will reach the grid of the tube l1 before the first portion a reaches the grid of the tube l8. The portion b of the double pulse will reach the grid of the tube I! at exactly the same time that the portion a will reach the grid of the tube l8 so that at this instant both grids are driven negatively, that of the tube I! by the portion b of the pulse and that of the tube l8 by the portion a of the pulse.

The cathodes of the tubes I! and I8 are connected to ground, as indicated, and the anodes are connected together and to a source of positive potential, indicated at 2|, through a resistor 22, the value of which is high as compared to the internal resistances of the tubes l1 and I8. A point 23 at the anode end of the resistor is then connected through the condenser 24 to the control circuit for the transmitter 10.

In the operation of the circuit, both tubes I1 and I8 are normally conductive. The point 23,.

therefore, will be at some potential less than the point 2| depending on the value of the resistor 22. Since the value of resistor 22 is high as compared to the internal resistances of the tubes [1 and I8, as long as either one tube or the other is conducting, the point 23 will remain at about the same potential, but, as soon as sufiiciently strong signals are received t cause both tubes to shut off together by the simultaneous application of the negative portion b of the double pulse on the grid of the tube l1 and the negative portion a of the double pulse on the grid of the tube 18, current ceases to fiow through resistor 22 and point 23 is raised to the potential of point 2|. Thus a positive potential is delivered through the condenser 24 to the control circuit.

Any combination of pulses which will cause the tubes l7 and I8 alternately to shut off will not deliver a positive pulse to the next stage; but as soon as a strong enough signal of the proper character to permit the tubes of both grids I1 and 18 to be driven negatively at the same time is received, the current through the resistor 22 is shut oif and the point 23 is driven in a positive direction. The double pulse indicated does not have to be used, since a single pulse having a greater time interval than the time delay of the grid circuit of tube i8 will also be capable of shutting off both tubes simultaneously.

Although the circuit of the present invention has been described as being incorporated in a beacon system, it will be appreciated that it may also have application elsewhere. Accordingly, the foregoing description should not be construed as definitive of the invention but merely illus trative of a possible application thereof. The spirit and scope of the invention is to be limited only by the appended claims.

What is claimed is:

1. A circuit for producing an output signal only upon application thereto of a pair of pulses having a predetermined time interval therebetween comprising, first and second electron tubes each having an anode, a cathode and a control grid, a source of anode potential for said tubes, at common anode resistor connected between the anodes of said tubes and said source of anode potential, said tubes being normally conductive and said resistor being of a value to produce a potential increase at said anodes only when both of said tubes are cut off simultaneously first and second means for applying pulse signals of negative polarity and the same wave form to the control grids of said first and second tubes, respectively, said first means comprising a conductor and said second means comprising a delay line having a delay time equal to said predetermined time interval.

2. A circuit for producing an output signal only upon application thereto of an input pulse of greater duration than a predetermined time comprising, a pair of electron tubes each havin at least an anode, a cathode and a control grid, means connecting the cathodes of said tubes together, a source of anode potential, a common load resistor connected between the anodes of said tubes and said source of anode potential, said tubes both being normally conductive and said resistor being of a value to produce a potential increase at the junction of said resistor and said anodes only when both tubes are simultaneously cut off, a conductor for applying said input pulses with negative polarity directly to the control grid of one of said tubes, and a delay line for applying said input pulses to the grid of the other tube with negative polarity and delayed relative to the application of said pulses to said one tube by an amount equal to said predetermined time.

LUIS W. ALVAREZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,252,599 Lewis Aug. 12, 1941 2,406,882 Young Sept. 3, 1 46 2,437,313 Bedford Mar. 9, 1948 2,522,609 Gloess Sept. 19, 1950 

